This invention relates to the field of semiconductor detectors for ionizing radiation dosage sensing and to the apparatus used for dosage detector read-out.
The radiation testing of electronic components and other military hardware during an underground nuclear detonation or a flash X-ray laboratory exposure calls for measurement instrumentation that provides quantative indications of radiation intensity and radiation duration. In the past it has been common to employ thermal luminescent detecting devices, semiconductor devices such as a PIN diode or transistors operating under a variety of algorithms, for these intensity and duration measurements. An interesting list of such prior art radiation detecting devices is presented in the U.S. patent of Takio Tomimasu et al, U.S. Pat. No. 4,147,934 together with a brief description of the advantages and limitations of such prior art radiation sensors.
The prior U.S. patent art also contains several examples of radiation detectors and associated read-out systems. The patent of G. L. Grundy et al, U.S. Pat. No. 3,479,509 for example discloses a junction transistor radiation detector usable in a pulsed nuclear radiation environment where X-ray, gamma ray and neutron bombardment effects are present. The Grundy apparatus utilizes radiation induced ions within a semiconductor element to effect a flux change in the saturable core of a blocking oscillator circuit and achieves a radiation intensity measurement by timing the delay between a radiation burst pulse and the blocking oscillator output pulse. It is especially notable that the Grundy invention relies on junction transistors which are normally biased into the non-conducting mode and reach transient conduction by way of radiation induced ions. These ions produce a transient forward bias of the base emitter junction in the transistor. The Grundy invention also uses the degree of transistor reversed bias and varying magnetic properties of the blocking oscillator feedback transformer as calibration adjustments for the radiation detector. Both the normally off sensing transistor and the use of a blocking oscillator read-out circuit are clear distinctions betweent the Grundy apparatus and the present invention.
The above mentioned patent of Takio Tomimasu et al. U.S. Pat. No. 4,147,934 is concerned with the use of a junction field effect transistor and the radiation induced noise in such transistors as a measurement of received ionizing radiation. Both the use of a junction field effect transistor radiation sensor and the noise based measurement algorithm distinguish the Tomimasu apparatus from the present invention.
The patent of Ronald G. Fraas, U.S. Pat. No. 4,213,045, concerns the use of a metal nitride oxide semiconductor (MMOS) transistor and the effect of radiation on a quantity of electrical charge stored at the boundary of a nitride layer as a radiation sensor. The Fraas invention employs a radiation read-out measurement which is based on sensing the treshold change in the MMOS transistor following a radiation dose. The field effect nature of the sensing transistor, the use of degradation of a stored charge, and employment of the threshold measuring read-out technique distinguish the Fraas apparatus from the present invention.
In the patent of Dale R. Koehler, U.S. Pat. No. 3,564,245, there is disclosed the use of a solid state radiation detector assembly which has a plurality of PN junction radiation sensing cells connected in parallel and electrically isolated by series connected semiconductor diodes. The use of single junction detector cells, an array of cells, and the isolation diode circuit distinguish the Koehler apparatus from the present invention.